1. Field of the Invention
The present invention relates to a hybrid induction motor having first and second magnetic rotors for improving a variable speed and driving characteristics, and more particularly, to a hybrid induction motor capable of reducing vibration and noise generated when the first and second magnetic rotors contact and as separated with each other as a motor is driven or is failed.
2. Description of the Related Art
FIG. 1 is a vertical sectional view of a hybrid induction motor studied and developed by the applicant of the present invention, FIG. 2 is a cross-sectional view showing the hybrid induction motor showing a state that the first and second magnetic rotors of FIG. 1 are combined while driven, and FIG. 3 is a cross-sectional view of the hybrid induction motor showing a state that the first and second magnetic rotors are separated while driven.
With reference to FIGS. 1 and 2, the hybrid induction motor studied and developed by the applicant of the present invention includes a motor casing 10; a rotational shaft 11 rotatably coupled with the motor casing 10; an induction rotor 20 having a rotor core 21 integrally coupled with the rotational shaft 11 and rotated and a conductor bar 22 inserted into the rotor core 21; a stator 70 having a hollow 70a to allow the induction rotor 20 to be inserted therein and having a certain length in a direction of the rotational shaft 11; a first magnetic rotor 40 inserted between the stator 70 and the rotor core 21 and coupled with the rotational shaft 11 so as to be freely rotatable; and a second magnetic rotor 40 inserted between the stator 70 and the induction rotor 20 in a symmetrical manner with the first magnetic rotor 40, and coupled with the rotational shaft 11 so as to be freely rotatable.
The motor casing 10 is a container with an opening and a cover 10a for covering the opening is coupled with the motor casing. A mounting recess 10b where a bearing 12 that rotatably supports the rotational shaft 11 is installed is formed at the cover 10a. 
The induction rotor 20 includes the rotor core 21 formed in an annular shape with a certain length and the conductor bar 22 inserted into the rotor core 21.
The rotor core 21 is a stacked body formed with a plurality of sheets stacked, and the rotational shaft 11 is fixed combined at the middle portion of the rotor core 21. Accordingly, when the rotational shaft 11 is rotated, the induction rotor 20 is also integrally rotated.
The stator 70 includes a stator core 71 formed with a certain length and a winding coil 72 having a main winding and a sub-winding wound in a circumferential direction within the stator core 71.
The stator core 71 is a stacked body formed by stacking a plurality of sheets and includes a yoke part 71a formed in an annular shape with a certain width and a plurality of teeth 71b extending with a certain length on an inner circumferential surface of the yoke part 71a. A slot 73 is formed between the teeth 71a and a hollow 70a in which the induction rotor 20 is inserted is formed within the stator core 71 by an end face of the teeth 71b. 
The winding coil 72 is wound on the teeth 71b several times and positioned in the slot 73 formed by the teeth 71b. When AC power is applied to the main winding and the sub-winding at an initial stage of driving, a rotating magnetic field is generated. At this time, an induction current flows to the conductor bar 22 of the induction rotor 20, and the induction rotor 20 starts to be rotated. Herein, the stator 70 is rotated by being slipped, and at this time, the current flowing at the sub-winding is blocked by a current blocking unit and current flows only at the main winding.
The first magnetic rotor 40 includes a first magnet in a cylindrical shape with a certain thickness and a first holder 42 formed in a cup shape and supporting the first magnet 41. The first magnet 41 is rotatably inserted between an inner circumferential surface of the first stator 70 and an outer circumferential surface of the induction rotor 20. A first bearing recess 42a in which the first bearing 42 is coupled is formed at one side of the first holder 42. As the rotational shaft 11 is coupled at the first bearing 43, the first holder 42 can be freely rotated on the rotational shaft 11.
The second magnetic rotor 50 includes a second magnet 51 installed spaced apart by a certain interval from the first magnet 41 and having a cylindrical shape with a certain thickness, and a second holder 52 formed in a cup shape and supporting the second magnet 51. The second magnet 51 is rotatably inserted between an inner circumferential surface of the second stator 80 and an outer circumferential surface of the inductor rotor 20. A second bearing recess 52a in which the second gearing 53 is coupled is formed at one side of the second holder 52. As the rotational shaft 11 is coupled with the second bearing 53, the second holder 53 can freely rotate on the rotational shaft 11.
The operation of the hybrid induction motor will now be described with reference to FIGS. 2 and 3.
When power is applied to the winding coil 72 of the stator 70, a rotating magnetic field is formed. The thusly formed rotating magnetic field makes the first and second magnetic rotors 40 and 50 rotate at a synchronous speed.
With reference to FIG. 2, when the S pole of the first magnet 41 and the N pole of the second magnet 51 are positioned at a position as shown in FIG. 2 while the motor is being driven, the S pole of the first magnet 41 and the N pole of the second magnet 51 attract each other. Then, the first magnetic rotor 40 moves in the direction of an arrow ‘A’0 and the second magnetic rotor 50 moves in a direction of an arrow ‘B’, allowing the first and second magnets 41 and 51 to be attached with each other, and in this case, vibration and noise are generated.
With reference to FIG. 3, when the S pole of the first magnet 41 and the S pole of the second magnet 51 are positioned at a position as shown in FIG. 3 while the motor is being driven, the S pole of the first magnet 41 and the S pole of the second magnet 51 repulses each other. Then, the first magnetic rotor 40 moves in a direction of an arrow ‘C’0 and the second magnetic rotor 50 moves in a direction of an arrow ‘D’, so as to be separated. At this time, while they are separated, vibration and noise are generated.
As a result, while the motor is being driven, the fist and second magnetic rotors 40 and 50 are continuously attached and separated to generate vibration and noise, causing a problem that the operational reliability of the hybrid induction motor is degraded.
In addition, the same problem also arises when the motor is broken down as well as when the motor is driven. Namely, when a power supply to the stator 70 is suddenly stopped because of a failure of the motor, the first and second magnets 41 and 51 are attached or separated according to mutual positions therebetween, generating vibration and noise. Thus, the operational reliability of the hybrid induction motor is also degraded.